Precursor Orbs
Precursor orbs are important part of "Jak 3" because they allow you to buy unlockable items throughout the game, such as increased ammo and invulnerability. For a cheat involving orbs, wait until time runs out and then hit the "square" button when the "failed mission" screen appears. You will then get three orbs. Repeat to gain more orbs.
Hero Mode
If you are playing in hero mode, you have the ability to skip some of the earlier missions in the game. Activate the turbo jetboard secret and then jump from island to island by hitting "L1" high jump and doing a forward flip. This will allow you to skip missions.
Damage
If you fall off a high place, hit the "circle" button right before you hit the ground. Doing so will stop you from receiving any damage from a high fall.
Easter Eggs
If you obtain all 600 precursor orbs in the game, you will win the ability to give Jak differently colored clothes. Not only will you unlock different colors, but you will also unlock different styles. You will be notified when you collect all 600 orbs.